Home automation requires several devices to communicate one with another to enable the user to control and command apparatuses, including luminaires, air conditioners. Devices like switches, light sensors, temperature sensors are controllers that are used to send commands to the controlled devices. Energy-harvesting controllers are an appealing option for the controls market. Indeed, these can be powered by the energy harvested from their environment (e.g. incident light, temperature difference or flow) or human action (e.g. button press), and thus autonomously operating, maintenance-free (no batteries need to be replaced) and have a “green appeal”.
One of the typical controls use cases, realized today with mains- and battery-powered wired or wireless controllers, is a multiple-rocker/multi-button controller (or switch/remote), allowing each of the rockers/buttons to control separate targets (actuator(s)), e.g. to control window side and corridor side lights of a room separately. This is illustrated by the exemplary FIG. 1, where a device 1 comprises two rockers 11 and 12 that control respectively at least one lamp 13 and 14 via on and off commands. It is to be noted that the number of rockers could be higher. Further, instead of a switch, the device could also include a light sensor or a motion detector. In fact, it does not only cover other user-actuation means (e.g. knobs, sliders, touchpads, etc.), but also multiple instances of autonomously operated devices, e.g. sensors, which may be triggered e.g. by a timer, the measured value passing a particular threshold, a particular amount of harvested energy, etc. However, for cost reduction reasons, it is envisaged to have only one wireless transceiver for the multiple different rockers/sensors each of which forms a distinct logical entity among multiple logical entities.
The Green Power feature of the ZigBee specification is currently the only standard for energy-harvesting wireless devices. It targets the full spectrum of energy-harvesting devices, from very simple ones just able to deliver a limited set of commands, to locally commissionable ones able to use security, to ones capable of bidirectional communication, i.e. remotely manageable. The Green Power Device (GPD) vendors can select the set of features required by their application—and possible with the energy source foreseen for their product.
The bidirectional communication feature of Green Power, i.e. the capability of sending a frame to (and receiving the frame by) the GPD, is tailored to the limited energy-resources of the Green Power Device. The GPD supporting the feature can, under application control, open a reception window for a short period of time after its own transmission (in the current GP specification v1.0, the gpRxOffset, defining the time between the start of the GPD's transmission and the start of the GPD's reception window, is 5 ms).
To make it possible, the devices communicating to the GPD have to behave as follows. The command to be delivered to the GPD needs to be buffered, in order to be ready for the GPD transmission. The Green Power specification defines the gpTxQueue for that purpose. Since the reception opportunities by the GPD may be scarce, despite the short time interval of gpRxOffset, the frame must be delivered securely; i.e. the device transmitting to the GPD has to verify that the received trigger frame is formatted correctly and protected according to the prior agreement with the GPD, and then security process the to be sent frame.
However, in the case of a single device with multiple logical entities like the device of FIG. 1, there is a need for adapting the addressing and communication schemes to enable an efficient and flexible communication. The same problem may occur with non ZigBee Green power devices, for example proprietary solutions.